BDNF and major depressive disorder: It was found that SNS may up-regulate CYP1A2, CYP2D1, CYP2E1, and CYP3A2 activity to reduce IL-6 and TNF-α expression, as well as up-regulation of BDNF and its receptor TrkB, reduce IL-1β, IL-6, and TNF-α expression to treat depression (Figure 6).